Osi layers networks
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OSI LAYERS-Networks. Tony Caleb D 14-July-2010. OSI: Open System Interconnection . Developed by the International Organization for Standardization in 1974. There are seven layers in OSI reference Model . It is a layered approach. OSI Reference Model. An Exchange using the OSI Layers.

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OSI LAYERS-Networks

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Osi layers networks

OSI LAYERS-Networks

Tony Caleb D

14-July-2010


Osi layers networks

OSI: Open System Interconnection .

Developed by the International Organization for Standardization in 1974.

There are seven layers in OSI reference Model .

It is a layered approach.

OSI Reference Model


Osi layers networks

An Exchange using the OSI Layers


Osi layers networks

Layer - 7

Upper Layer

or

Software Layer

Lower Layer

or

Hardware Layer

Layer - 6

Layer - 5

Heart of OSI

Layer - 4

Layer - 3

Layer - 2

Layer - 1

OSI Reference Model

Application

Presentation

Session

Transport

Network

Data Link

Physical


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Application Layer

Application Layer is responsible for providing Networking Services to the user. It is also known as Desktop Layer. Identification of Services is done using Port Numbers.

Ports are Entry and Exit Points to the Layer

Total No. Ports 0 – 65535

Reserved Ports 0 – 1023

Open Client Ports 1024 – 65535

Application


Osi layers networks

Client

Client

Web Server

Web Server

Example of HTTP request

http://www.zoomgroup.com


Osi layers networks

Client

Web Server

Example of HTTP request

HTTP Request

http:// www.zoomgroup.com

Webpage

HTTP Request

Listen on

Port 80

Sending HTTP Reply

Webpage

Received HTTP Reply

http://www.symantec.com

Webpage


Osi layers networks

Examples of Networking Services

Service Port No.

HTTP 80

FTP 21

SMTP 25

TELNET 23

TFTP69


Osi layers networks

Presentation

80

21

25

53

67

69

Session

Transport

Network

Data Link

Physical

Data flow from Application Layer

Application

Data


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Presentation Layer

Presentation Layeris responsible for converting data into standard format.

Examples : JPEG, MPEG, MIDI, WAV, MP3

Following tasks are perform at Presentation layer :

Encoding – Decoding

Encryption – Decryption

Compression – Decompression

Presentation


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Data flow from Presentation Layer

Data

Data


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Session Layer

Session Layer is responsible for establishing, maintaining and terminating session.

Session ID works at Session Layer.

Examples :

RPC  Remote Procedure Call

SQL  Structured Query Language

NFS  Network File System

Session


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Data flow from Session Layer

Data

Data

Data


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Transport Layer

  • Transport Layer is responsible for end-to-end connectivity. It is also known as the heart of OSI Layers. Following tasks are performed at the Transport Layer : -

    • Identifying Service

    • Multiplexing & De-multiplexing

    • Segmentation

    • Sequencing & Reassembling

    • Error Correction

    • Flow Control

Transport


Osi layers networks

TCP

UDP

  • Transmission Control Protocol

  • Connection Oriented

  • Acknowledgement

  • Reliable

  • Slower

  • Port No. 6

  • e.g. HTTP, FTP, SMTP

  • User Datagram Protocol

  • Connection Less

  • No Acknowledgement

  • Unreliable

  • Faster

  • Port No. 17

  • e.g. DNS, DHCP, TFTP

Identifying Service


Osi layers networks

Multiplexing & De-multiplexing


Osi layers networks

Application

Presentation

Session

80

21

25

53

67

69

Network

Data Link

TCP - 6

UDP - 17

Physical

Multiplexing & De-multiplexing

Transport


Osi layers networks

A

B

Segmentation

Hello! How are you ?

Hello! How are you ?

Hello!

How

Are

You

?


Osi layers networks

you Hello! How ? are

A

B

Sequencing & Reassembling

Hello! How are you ?

Hello! How are you ?

You Hello! How ? Are

You

Hello!

How

?

Are

Hello!

Are

You

?

How


Osi layers networks

Hello! How are you ?

A

B

Sequencing & Reassembling

Hello! How are you ?

Hello! How are you ?

Hello! How are you ?

Hello!

1/5

Hello!

1/5

Are

3/5

Are

3/5

You

4/5

You

4/5

?

5/5

?

5/5

How

2/5

How

2/5

You

4/5

Hello!

1/5

How

2/5

?

5/5

Are

3/5


Osi layers networks

Hello!

1/5

Are

3/5

You

4/5

?

5/5

Hello! How are you ?

A

B

ErrorCorrection

Segment Missing

Hello! How are you ?

Hello! How are you ?

Hello! How are you ?

Hello!

1/5

Hello!

1/5

Are

3/5

Are

3/5

You

4/5

You

4/5

?

5/5

?

5/5

How

2/5

How

2/5

You

4/5

Hello!

1/5

?

5/5

Are

3/5

How

2/5


Osi layers networks

A

B

Flow Control - Windowing

Sending 3-window

Received 3-window

PC-A

can send 4 Segments at a time to

PC-B

Ack. Received-4

Ack-Rec-3

Sending

5-window

Received 4-window


Osi layers networks

Application

Presentation

Session

Transport

TH

Network

Data Link

Physical

Data flow from Transport Layer

Data

Data

Data

Segment

Data


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Network Layer

  • Network Layer is responsible for providing best path for data to reach the destination. Logical Addressing works on this layer. Router is a Network Layer device.

  • It is divided into two parts

    • Routed Protocols

    • e.g. IP, IPX, Apple Talk.

    • Routing Protocols

    • e.g. RIP, IGRP, OSPF, EIGRP

Network


Osi layers networks

Segment

Hello! How are you ?

Segment

A

B

192.168.1.1

192.168.1.2

Routed Protocols

Segment

Hello! How are you ?

Source IP

192.168.1.1

Destination IP

192.168.1.2

Source IP

192.168.1.1

Destination IP

192.168.1.2


Osi layers networks

A

Routing Protocols

www.symantec.com


Osi layers networks

Hop to Hop Delivery


Osi layers networks

IP Addresses


Osi layers networks

Application

Presentation

Session

Transport

e.g. Router

Network

NH

Data Link

Physical

Data flow from Network Layer

Data

Data

Data

Segment

Packet

Segment


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Data link Layer

  • Datalink Layer is divided into two Sub

    • LLC – Logical Link Control

    • It talks about Wan protocols e.g. PPP, HDLC, Frame-relay

    • MAC – Media Access Control

    • It talks about Physical Address. It is a 48 bit address i.e. 12 digit Hexadecimal Number.

    • It is also responsible for Error Detection

    • Devices working on Data Link Layer are Switch, Bridge, NIC.

Data Link


Osi layers networks

Packet

A

B

192.168.1.1

00-20-18-C0-07-71

192.168.1.2

00-20-18-C0-07-72

Error Detection – CRC Check

PC-A

CRC No. 33333

PC-B

CRC No. 11114

Error Detected

For Error Correction

Contact Source Transport layer

Packet

Hello! How are you ?

00000

11114

46323

99434

89696

99323

55434

00000

43434

32434

43434

32434

55434

99323

22222

99434

46323

11114

Error Detected

Source MAC

00-20-18-C0-07-71

Destination MAC

00-20-18-C0-07-72

22222

89696

33333


Osi layers networks

Packet

Hello! How are you ?

Packet

A

B

192.168.1.1

00-20-18-C0-07-71

192.168.1.2

00-20-18-C0-07-72

Error Detection – CRC Check

Packet

22222

22222

00000

20202

99323

46323

99434

43434

89696

11114

99323

46323

43434

99434

55434

11114

20202

Source MAC

00-20-18-C0-07-71

Destination MAC

00-20-18-C0-07-72

32434

00000

Source MAC

00-20-18-C0-07-71

Destination MAC

00-20-18-C0-07-72

55434

89696

32434


Osi layers networks

Application

Presentation

Session

Transport

Network

e.g. Switch

Data Link

DH

DT

Physical

Data flow from Data Link Layer

Data

Data

Data

Segment

Packet

Frame

Packet

Packet


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Physical Layer

Physical Layer is responsible for electrical, mechanical and procedural checks. Data will be converted into Binary (i.e) 0’s & 1’s. Data will be in the form of electrical pulses if it is Coaxial or Twisted Pair cable and in the form of Light if it is Fiber Optic Cable.

Devices working at Physical Layer are Hubs, Repeaters, Cables, Modems etc.

Physical


Osi layers networks

Frame

Hello! How are you ?

Frame

A

B

Physical Layer Example

Frame

1010101010101010

1010101010101010

1010101101010101010101010

0101011010101010101010101

1010101101010101010101010

0101011010101010101010101

0101011010101010101010101


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

e.g. Hub

Physical

Data flow from Physical Layer

Data

Data

Data

Segment

Packet

Frame

Bits


Osi layers networks

A

B

Application

Application

Presentation

Presentation

Session

Session

Transport

Transport

TH

TH

TH

Data

Network

Network

Segment

NH

NH

NH

Data Link

Data Link

Packet

DH

Packet

DH

DH

DT

DT

DT

Physical

Physical

Data Encapsulation & De-capsulation

Data

Data

Data

Data

Data

Data

Segment

Segment

Data

Packet

Packet

Segment

Frame

Frame

Packet

Packet

Bits

Bits


Osi layers networks

Application

Presentation

Session

Transport

Network

Data Link

Physical

Comparing OSI with TCP/IP Layers

OSI Layers

TCP/IP Layers

Application

Transport

Internet

Network

Access


Osi layers networks

Relationship Between Layers and Address in TCP/IP


Osi layers networks

Summary of layers


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